140 THE PROTEIN SUBSTANCES. 



The phenylisocyanate melts at 147, and on boiling with 20-per cent 

 hydrochloric acid for a short time, it is changed into d-phenyliso- 

 propyl hydantoin, which melts at 131-133 C. 



Leucine (aminocaproic acid, or, more correctly, a-aminoisobutylacetic 

 CH 3 CH 3 



acid), C 6 Hi 3 NO 2 = CH 2 , is produced from protein substances in 



CH(NH 2 ) 



COOH 



their hydrolytic cleavage by proteolytic enzymes, by boiling with dilute 

 acids or alkalies or by fusing with alkali hydroxides, and by putrefaction. 

 There are also observations that indicate that in the hydrolysis besides 

 the ordinary leucine perhaps also normal leucine may be formed (HECKEL 

 .and SAMEC 1 ). 



Because of the ease with which leucine (and tyrosine) are formed 

 in the decomposition of protein substances, it is difficult to decide pos- 

 itively whether these bodies when found in the tissues are constituents 

 of the living body or are to be considered only as decomposition products 

 formed after death. Leucine, it seems, has been found as a normal 

 constituent of the pancreas and its secretion, in the spleen, thymus, and 

 lymph glands, in the thyroid gland, in the salivary, glands, in the kidneys 

 and in the liver. It also occurs in the wool of sheep, in dirt from the skin 

 (inactive epidermis), and between the toes, and its decomposition prod- 

 ucts have the disagreeable odor of the perspiration of the feet. It is 

 found pathologically in atheromatous cysts, ichthyosis scales, pus, blood, 

 liver, and urine (in diseases of the liver and in phosphorus poisoning). 

 Leucine occurs often in invertebrates and also in the plant kingdom. On 

 hydrolytic cleavage various protein substances yield different amounts 

 of leucine, as shown in the tables given on pages 106, 107, 114 and 124. 

 From the figures there given we call attention to the following: ERLEN- 

 MEYER and SCHOFFER obtained 36-45 per cent leucine from the cervical 

 ligament, COHN obtained 32 per cent from casein, E. FISCHER and 

 ABDERHALDEN 20 p^r^ cent from haemoglobin, and FISCHER and 

 DORPINHAUS 18.3 per cent from horn substance. 2 



The leucine obtained by cleavage of protein substances is generally 

 Z -leucine, which is levorotatory in water solution and dextrorotatory in 

 ,acid solution. The leucine prepared synthetically by HtJFNER 3 from 



1 Heckel, Monatsh. f. Chem., 29; Samec, ibid., 29. 



2 Erlenmeyer and Schoffer, cited from Maly, Chem. d. Verdauungssafte, in Her- 

 mann's Handb. d. Physiol., 5, Theil 2, p. 209; Cohn, Zeitschr. f. physiol. Chem., 22; 

 Fischer and his collaborators, ibid., 36. 



3 Journ. f. prakt. Chem. (N. F.), 1. 



